Jean Aimé Mbey

This study investigates the influence of kaolinite crystallinity on the direct synthesis of hydroxysodalite from kaolin.

This study investigates the influence of metakaolin mass fraction in sodium hydroxide solution on the structure of silica gels produced by the sol-gel method. The effect of this ratio was analyzed using Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and differential scanning calorimetry coupled with thermogravimetry (TG-DSC). The results revealed that after calcination at 650 °C, there is a complete conversion of kaolinite to amorphous metakaolinite. XRD analyses of the gels show a characteristic halo of amorphous silica with some crystalline reflections mainly associated to halite. The evaluation of this influence indicates that better dispersion of metakaolin promotes interactions that lead to the hydrolysis of sodium silicate and grain growth. At constant soda solution volume, the increase of metakaolin mass fraction reduced the formation of halite as by-product while a starting crystallization toward hydroxysodalite like structure is observed. This was associated to the formation of short chains oligomers within the gel network as the metakaolin mass increase. These short chains exhibit more hydroxyl groups, which are beneficial for optimizing the retention of polar compounds such as water.

This study presents a detailed mineralogical and crystallochemical characterisation of clay deposits from Mbengwi (Northwest Region, Cameroon) to evaluate their suitability for industrial applications. Three samples collected at depths of 10.7 m (BGW1), 8.8 m (BGW2) and 6.5 m (BGW3) were analysed using x-ray fluorescence, x-ray diffraction, Fourier-transform infrared spectroscopy (FTIR), thermogravimetric analysis and differential scanning calorimetry. Across all sampled depths, high-purity kaolinite consistently dominates the mineralogical composition (∼90%), with minor occurrences of illite (1.5%), quartz (3%), goethite (1.3%) and anatase (1.4%). The SiO ₂ /Al ₂ O ₃ ratio closely aligns with the theoretical value for ideal kaolinite (1.17). The absence of distinct crystalline iron-bearing phases suggests either isomorphic substitution of Fe ³⁺ within the kaolinite lattice or the presence of poorly crystalline iron minerals. Crystallinity indices – including the Hinckley Index, the size of the coherent scattering domain (D), the slope ratio and the FTIR-derived P ₀ and P ₂ factors – indicate a progressive enhancement of structural order with increasing depth. Thermal analyses corroborate this trend: deeper samples exhibit higher dehydroxylation temperatures and sharper endothermic peaks, reflecting least defect density and high kaolinite purity. These findings highlight the superior crystallinity and purity of deeper kaolinitic layers, positioning Mbengwi clays as promising candidates for high-performance applications such as ceramics, paper, catalyst supports and polymer industries.

Cette étude porte sur des films composites à base d'amidon de manioc plastifié au glycérol et d'une argile kaolinique, comme charge minérale. L'origine et les mécanismes des interactions argile-amidon et leur rôle sur les propriétés des films ont été examinés. Pour vaincre le caractère non-expansible de la kaolinite, l'analyse du mécanisme de son exfoliation a été effectuée par insertion du diméthylsulfoxyde suivi d'un échange en milieux acétate d'éthyle et acétate d'ammonium. Une forte déstructuration de l'édifice cristallin de la kaolinite suite à l'échange est observée. La réassociation des feuillets après échange est désordonnée et permet d'escompter une meilleure dispersion de la kaolinite intercalée au sein d'un polymère. Ceci est confirmé par les analyses comparées de microscopies et de diffraction des rayons X sur des films incorporant diverses doses d'argile brute ou intercalée. L'abaissement de la température de transition vitreuse et du module élastique, ainsi que l'accroissement des effets de barrières à la décomposition thermique, à la diffusion de vapeur d'eau et à la transmission des UV visibles confirme la dispersion meilleure de la kaolinite intercalée. L'orientation des chaînes d'amidon et la diffusion du plastifiant transporté à l'interface par l'argile sont les mécanismes qui justifient l'effet plastifiant apporté par l'argile. L'interférence des interactions amidon-argile sur les interactions chaîne-chaîne au sein de l'amidon participe à la plasticité des films en diminuant la cristallinité. Les interactions amidon-argile se sont avérées faibles du fait des répulsions électrostatiques associées à des interactions associatives de type pont hydrogène

The environmental pollution caused by the mismanagement of household waste dumps and their leachate in developing countries has led researchers to explore adsorption treatment processes using shales from Côte d'Ivoire. To carry out this study, mineralogical characterization by X-ray Diffraction and Infrared of the shales was required prior to treatment. Using humic acid extracted from the leachates, adsorption tests were carried out using batch adsorption tests, and the optimum adsorption parameters were determined and modeled. The results of the mineralogical characterization revealed the presence of certain minerals. Batch adsorption treatment using slate from Côte d'Ivoire showed that the optimum concentration of slate to use was 30 g/L for a concentration of 15 mg/L humic acid. The duration of agitation at equilibrium was 60 minutes, with a maximum adsorption rate of 92 %. The effect of pH on the adsorption of humic acids showed that, in general, the evolution of adsorption rates was inversely proportional to the increase in pH. The highest yields were obtained at pH levels between 3.5 and 5.5. The results of the influence of the initial concentration of humic acids showed an increase in adsorption efficiency with the increase in the initial concentration up to 100 mg/L. The pseudo-second order model better described the adsorption of humic acid on the shale; it is accompanied by intra-particle diffusion, therefore by a contribution of active sites inside the pores.

Correction for ‘Synthesis of an exfoliated kaolinite–poly(urea–formaldehyde) nanocomposite’ by Hervé Barye Tatang et al., RSC Adv., 2025, 15, 3026–3039, https://doi.org/10.1039/D4RA08707K.

Kaolinite–poly(urea–formaldehyde) nanocomposite was successfully prepared under ambient conditions, by simply immersing kaolinite-urea complex in formaldehyde. A self-healing behavior is observed for the polymer within the nanocomposite.